Nonspecific immunoregulatory lymphokines and monokines, among them IDS (inhibitor of DNA synthesis), LAF (lymphocyte-activating factor), and MF (mitogenic factor), and possibly other specific immunoregulatory substances, will be studied for their mode of action on target lymphocytes and other cells. Effects will be examined on different phases of the cell cycle in dividing cells, on lymphokine production, on cell-mediated lymphocytotoxicity, and on immunoglobulin production, and the role of second messengers such as prostaglandins, cyclic AMP, and cyclic GMP evaluated.